CN108604639B - Organic optoelectronic devices, arrays of such devices, and methods of making such arrays - Google Patents

Abstract

The optoelectronic device (1) comprises a stack of layers arranged on an electrically insulating substrate (2), the stack comprising at least a cathode (3) having a work function of

made of material; an electron collection layer (4), which is arranged on the cathode (3) and consists of a work function of

The sheet resistance is R; the active layer (5) includes at least one p-type organic semiconductor material, the p-type organic semiconductor material has an energy level HO1, and is characterized in that: the electron collection layer (3) ) of the work function

The energy level HO1 of the active layer (5) forms a potential barrier capable of preventing the injection of holes from the cathode (3) into the active layer (5), and the electron collection layer (4) The sheet resistance R is greater than or equal to 10 ⁸ Ω.

Description

Organic optoelectronic devices, arrays of such devices, and methods of making such arrays

technical field

The present invention relates to organic optoelectronic devices and to matrices of such devices, ie to matrices of photodetectors (pixilated imagers) or display matrices. The invention is particularly (but not exclusively) suitable for the production of large area matrix X-ray imagers based on the principle of indirect detection and preferably using organic semiconductors, the possible applications of which are medical radiology, non-destructive testing and security screening.

Background technique

In the field of X-ray imaging, two detection modes are commonly used. The first mode, called the direct detection mode, utilizes a matrix of photodetectors, each capable of converting the X-rays it absorbs into electrical charges. The second mode, called indirect mode, first converts X-rays into visible photons through a scintillator, and then converts the resulting visible photons into electrical charges using a matrix of photodetectors. The present invention relates to a matrix of pixels for indirect detection of X-rays, each pixel consisting of at least one thin film transistor (TFT) coupled to an organic photodetector. In each pixel, a transistor is typically connected to the first electrode of the organic photodetector.

A layer suitable for light conversion of light is typically deposited on the first electrode. The layer may be organic, for example, and comprise a nanostructured mixture of p-type and n-type semiconductors (Li, G., Shrotriya, V., Huang, J., Yao, Y., Moriarty, T., Emery, K. , & Yang, Y., 2005, High-efficiency solution processable polymerphotovoltaic cells by self-organization of polymer blends, Nature materials, 4(11), 864-868). Then, the upper electrode is deposited on the light conversion layer.

FIG. 1 schematically shows the structure of an organic photodiode according to the prior art. The stack comprises, for example, a transparent substrate (made of glass, polyethylene naphthalate (PEN) or polyethylene terephthalate (PET)). The substrate is covered by a transparent metal electrode, eg made of indium tin oxide (ITO), and then by a hole collecting layer (HCL) capable of collecting holes during irradiation, eg of poly(3,4-substrate) Ethyldioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). These layers are covered by layers suitable for light conversion, referred to as active layers, and fabricated as described above. Finally, the active layer is covered by an electron collecting layer (ECL), eg made of aluminum. In the example shown in Figure 1, the photodiode is illuminated through a transparent substrate: this illumination pattern and the structure of the photodiode are said to be direct. The layers for transporting carriers are electrically connected to the layers for collecting carriers (HCL and ECL). In the direct structure shown in Figure 1, the transport of holes is achieved through the ITO layer and the transport of electrons is achieved through the aluminum layer.

FIG. 2 schematically shows an organic photodiode of a so-called flip-chip structure according to the prior art. The photodiode shown includes a transparent substrate covered by a transparent electron transport layer (ETL), which itself is covered by a transparent electron collection layer (ECL). These layers are covered by an active layer and a hole collecting layer (HCL). The HCL is for example covered by a silver layer whose function is to allow hole transport (HTL) and to reflect incident light from the substrate. ECL is for example made of zinc oxide (ZnO) or titanium oxide (TiOx), HCL is for example made of poly(styrene sulfonate) (PEDOT:PSS) or of metal oxides such as molybdenum oxide, tungsten oxide or vanadium oxide to make. Structures of this type have been disclosed by Jeong, J. et al., Inverted Organic Photodetectors With ZnO Electron-Collecting Buffer Layers and Polymer Bulk Heterojunction Active Layers, Selected Topics in Quantum Electronics, IEEE Journal of, 20(6), 130-136.

In both direct or flip-chip photodiode structures, light may be absorbed by different layers, especially by the upper and/or lower electrodes.

It is desirable to fabricate a matrix of flip-chip organic photodiodes as described above for medical imaging applications. This type of imaging requires a very low detection threshold. One of the ways to achieve a low detection threshold is to limit or even suppress the dark current of the photodiode, ie the residual current of the photodiode in the absence of illuminated light when the photodiode is biased. If the work function of the material of the electron collection layer is too high, parasitic injection of holes from this layer into the donor of the active layer is promoted. One prior art solution is to make the lower electrode (the electrode in contact with the substrate) from a metal whose work function is lower than that of commonly used materials (usually ITO). For example, the work functions of aluminum and chromium are lower than those of ITO. These materials have the disadvantage of being unstable in the presence of air because they are prone to oxidation.

This technical problem can be partially solved (as described by Jeong, J. et al.) by using an electron collecting layer (which is in the gap between the lower electrode and the active layer), which acts to reduce the interaction with the active layer. Work function of the material with which the layers are in contact: Zinc oxide (ZnO) can be used for this. The ZnO used is a semiconductor: its use in full area deposition (without pattern-defining lithography steps) is technically problematic due to the potential for leakage currents between the different pixels of the matrix of photodiodes. A defective pixel (eg, where the work function is occasionally unsuitable for the active layer) may induce leakage currents in all adjacent pixels and render the pixel area surrounding the defective pixel unsuitable for imaging. A photolithographic step enabling the electron collection layer to be etched to electrically separate the individual pixels may be one solution. This step is undesirable in a manufacturing process where having too many consecutive lithography steps required affects the production of the device and/or its manufacturing yield.

SUMMARY OF THE INVENTION

The present invention aims to remedy the above-mentioned drawbacks of the prior art, and more particularly, to manufacture matrix organic optoelectronic devices with minimized leakage current, while enabling the number of photolithographic steps performed during the manufacture of such devices to be limited.

A subject of the present invention capable of achieving this objective, in whole or in part, is an optoelectronic device comprising a stack of planar thin layers arranged on an electrically insulating substrate, said stack comprising at least:

- a cathode made of a material with a work function _ΦC ;

- an electron collecting layer arranged above said cathode and made of a material with work function Φ ₁ and sheet resistance R;

- an active layer comprising at least one p-type organic semiconductor, and an n-type semiconductor, said layer being suitable for emitting or detecting light, and being arranged above said electron collecting layer, the highest occupancy of said p-type organic semiconductor The energy level of the molecular orbital is HO1;

- a hole collecting layer disposed over the active layer; and

- an anode arranged above said hole collecting layer;

It is characterized by:

- the work function Φ1 of the electron collection layer and the energy level _HO1 of the active layer form a potential barrier capable of preventing the injection of holes from the cathode into the active layer; and

- the sheet resistance R of the electron collecting layer is greater than or equal to 10 ⁸ Ω.

Advantageously, the work function Φ ₁ of the electron collecting layer of the device is strictly smaller than the work function Φ _C of the cathode.

Advantageously, said material of said electron collecting layer of the device is selected from zinc oxide and titanium oxide.

Another subject of the invention is a matrix optoelectronic device comprising a plurality of optoelectronic devices and an electron collection layer, the electron collection layer being common to at least a portion of the optoelectronic devices, and in each of the optoelectronic devices are substantially continuous.

Advantageously, in said material of said common electron collecting layer, the sheet resistance R of said common electron collecting layer of a matrix optoelectronic device is capable of preventing electrical resistance between said part or parts of said optoelectronic devices. carrier current.

Advantageously, the resistivity of the material of the common electron collection layer of the matrix photovoltaic device is lower in the thickness direction of the electron collection layer than in the principal plane direction of the electron collection layer.

Advantageously, the common electron collecting layer of the matrix optoelectronic device comprises crystallites arranged in columns in the thickness direction of the electron collecting layer.

Advantageously, the matrix optoelectronic device comprises at least one stabilization layer arranged between said common electron collection layer and at least one active layer, wherein said stabilization layer is capable of reducing the resistivity of the material of said common electron collection layer Dependence on brightness.

Advantageously, the material of the stabilization layer of the matrix photovoltaic device is an opaque oxide preferably selected from tin oxide and palladium oxide.

Advantageously, the material of the common electron collection layer of the matrix photovoltaic device comprises a p-type dopant.

Advantageously, the p-type dopant is selected from palladium, cobalt, copper and molybdenum.

Advantageously, at least one of said electron collecting layers of said matrix optoelectronic device comprises metal oxide nanoparticles and a polar polymer, said polar polymer being attached to said metal oxide nanoparticles.

Advantageously, at least one element selected from the group consisting of the substrate, cathode, electron collecting layer, active layer, hole collecting layer and anode of the matrix photovoltaic device is transparent.

Advantageously, the matrix optoelectronic device comprises a layer of scintillator material arranged over each of the anodes.

Another subject of the invention is a process for the manufacture of an optoelectronic device comprising a stack of planar thin layers arranged on an electrically insulating substrate, the stack comprising at least:

- a cathode made of a material with a work function _ΦC ;

- an electron collecting layer arranged above said cathode and made of a material with work function Φ ₁ and sheet resistance R;

- an active layer comprising at least one p-type organic semiconductor, and an n-type semiconductor, said active layer being suitable for emitting or detecting light and arranged over said electron collecting layer, said p-type organic semiconductor The energy level of the highest occupied molecular orbital is HO1;

- a hole collecting layer disposed over the active layer; and

- an anode arranged above said hole collecting layer;

The process comprises depositing at least a portion of the material of the electron collecting layer by cathode sputtering in an atmosphere comprising at least 1% and preferably at least 2% by mass molecular oxygen at a temperature between 0°C and 100°C. a step.

Another subject of the invention is a process for the manufacture of an optoelectronic device comprising a stack of planar thin layers arranged on an electrically insulating substrate, the stack comprising at least:

- a cathode made of a material with a work function _ΦC ;

- an electron collecting layer arranged above said cathode and made of a material with work function Φ ₁ and sheet resistance R;

- an active layer comprising at least one p-type organic semiconductor, and an n-type semiconductor, said active layer being suitable for emitting or detecting light and arranged over said electron collecting layer, said p-type organic semiconductor The energy level of the highest occupied molecular orbital is HO1;

- a hole collecting layer disposed over the active layer; and

- an anode arranged above said hole collecting layer;

The process includes at least one step of forming the electron collecting layer using a sol-gel method including the step of depositing a solution comprising a precursor polymer selected from metal acetic acid Salts, metal nitrates and metal chlorides.

Advantageously, the solution includes p-type dopants.

Another subject of the invention is a process for the manufacture of a matrix optoelectronic device comprising a plurality of optoelectronic devices arranged in a pattern, said optoelectronic device comprising a stack of planar thin layers arranged on an electrically insulating substrate, whereby The stacking includes at least:

- a cathode made of a material with a work function _ΦC ;

- a common electron collecting layer comprising a first sublayer and a plurality of second sublayers, said common electron collecting layer being arranged over each of said cathodes and consisting of a work function Φ ₁ , a sheet resistance Made of R material;

- an active layer comprising at least one p-type organic semiconductor, and an n-type semiconductor, said active layer being suitable for emitting or detecting light and arranged over said electron collecting layer, said p-type organic semiconductor The energy level of the highest occupied molecular orbital is HO1;

- a hole collecting layer disposed over the active layer; and

- an anode arranged above said hole collecting layer;

The process includes at least two sub-steps of depositing the electron collecting layer, the two sub-steps including:

- depositing a first common electron collecting sublayer;

- depositing a plurality of second sublayers in a pattern corresponding to the pattern of the optoelectronic device.

Description of drawings

The invention will be better understood and other advantages, details and features of the invention will become apparent from the following explanatory description given by way of example with reference to the accompanying drawings, wherein:

- Figure 3 schematically shows the structure of a flip-chip optoelectronic device according to an embodiment of the invention;

- Figure 4 shows a band diagram corresponding to the structure of a photovoltaic device according to the prior art;

- Figure 5 shows a band diagram of a structure corresponding to an embodiment of the invention;

- Figure 6 schematically shows a matrix optoelectronic device according to an embodiment of the invention;

- Figure 7 schematically shows a top view of a matrix optoelectronic device according to an embodiment of the invention;

- Figure 8 schematically shows a cross-sectional view of a part of an optoelectronic device comprising an electron collecting layer comprising crystallites;

- Figure 9 schematically shows a thin layer arranged on a substrate of a matrix photovoltaic device according to an embodiment of the invention;

- Figure 10 shows a graph of the change in the concentration of the precursors of the normalized sol-gel reaction;

- Figure 11 shows schematically the effect of the size of the precursor polymer on the distance between the ZnO particles;

- Figure 12 shows schematically the reduction in electrical conductivity in the presence of organic residues in the electron collecting layer;

- Figure 13 schematically shows a matrix photovoltaic device in which the resistance of the electron collecting layer is increased by a step of etching said layer; and

- Figure 14 shows an embodiment of the invention in which a matrix optoelectronic device comprises a layer of scintillator material.

Detailed ways

FIG. 1 schematically shows the structure of a prior art optoelectronic device. The device shown is a direct structure photodiode as described above.

FIG. 2 schematically shows an organic photodiode of a so-called flip-chip structure according to the prior art.

3 schematically shows the structure of an optoelectronic device 1 having a flip-chip structure according to an embodiment of the present invention; the optoelectronic device 1 includes a transparent substrate 2 from below which the optoelectronic device 1 can be illuminated. Transparent means being able to transmit, in whole or in part, electromagnetic waves whose wavelengths are included in the visible and/or near-ultraviolet and/or near-infrared range. Illumination is indicated by upward black arrows in Figure 3. The substrate 2 can be made of glass, PEN or PET. The stack of planar thin layers which partially form the optoelectronic device 1 is arranged on the substrate 2 .

The cathode 3 is arranged on the substrate 2 . The cathode 3 is made of a material whose work function is denoted _ΦC . In an embodiment of the present invention, the cathode 3 may be made of ITO. In this structure, the cathode 3 can also function as an electron transport layer or ETL.

The electron collection layer 4 is arranged over the cathode 3 . The work function of the material of the electron collecting layer 4 is denoted Φ ₁ and the sheet resistance of the electron collecting layer 4 (measured in Ω/□ and/or in Ω) is denoted R. In an embodiment of the invention, R is strictly greater than 10 ⁸ Ω, preferably strictly greater than 10 ¹⁰ Ω and preferably strictly greater than 10 ¹¹ Ω. The electron collection layer 4 may be made of titanium oxide (TiOx) or zinc oxide (ZnO).

The active layer 5 is arranged over the electron collection layer 4 . The active layer 5 comprises at least one p-type organic semiconductor (the energy level of which the highest occupied molecular orbital is labeled HO1), and an n-type semiconductor, and is suitable for emitting or detecting light. The active layer 5 is arranged on the electron collecting layer 4 . The active layer 5 includes, for example, a mixture of polymers and fullerenes. The active layer 5 is deposited by a coating operation, for example, with a solvent of 1,3,5-trimethylbenzene, and has a dry thickness of 200 nm after thermal annealing. This layer is a 1:2 mass ratio of electron donor material (head-to-tail linked poly(3-hexylthiophene), known as P3HT RR) and electron acceptor material (bis[1,4]methanenaphtho[1] ,2:2',3';56,60:2",3"][5,6]-fullerene-C60-Ih, called ICBA). The active layer 5 may cover the entire matrix. The active layer 5 can also be deposited by spraying with a chlorobenzene type solvent with a dry thickness of 800 nm after thermal annealing. The layer can also be an electron-donor material (poly[(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b)) in a mass ratio of 1:2 ')dithiophene)-2,6-diyl-alternate-(4-(2-ethylhexyl)-thieno[3,4-b]thiophene-)-2-6diyl)], known as PBDTTT -C) A nanostructured mixture between an electron acceptor material ([6,6]-phenyl-C71-butyric acid methyl ester, known as [70]PCBM).

A hole collection layer (HCL) 6 is arranged over the active layer 5 . In an embodiment of the present invention, the hole collection layer 6 is made of a material selected from the group consisting of PEDOT:PSS, molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), and vanadium oxide (V ₂ O ₅ ).

The anode 7 is arranged above the hole collecting layer 6 . In one embodiment of the invention, the anode is a metal reflector, eg made of silver, which has the advantage of increasing the efficiency of the photovoltaic device 1 . The anode can also act as a hole transport layer HTL.

In an embodiment of the present invention, the work function Φ1 of the electron collection layer ₄ and the energy level of the highest occupied molecular orbital of the p-type material of the active layer 5 (which is labeled as HO1 ) form a structure capable of preventing the injection of holes from the cathode 3 The potential barrier of the active layer 5 . The barrier is strictly greater than 0.3 eV, preferably strictly greater than 0.4 eV, and preferably strictly greater than 0.5 eV. A detailed description of the energy levels of the different layers of the device is depicted in FIG. 5 .

In one embodiment of the invention, the optoelectronic device is adapted to be illuminated from above. The anode 7 can be transparent in this case. This embodiment can avoid scattering of incident light through the substrate, and can achieve better resolution in the case of a matrix arrangement of a plurality of optoelectronic devices 1 .

FIG. 4 shows an energy band diagram corresponding to the structure of an optoelectronic device according to the prior art. The work function of anode 7 (labeled Φ _A ) and the work function of cathode 3 (labeled Φ _C ) are defined by the energy difference between the Fermi level and the vacuum level E ₀ of the material of each layer. The electron affinity of the active layer 5 is defined by the energy difference between the lowest unoccupied molecular orbital of the active layer ₅ (called BV or LUMO) and the vacuum level E0, and for the donor material of the active layer 5 11 and the acceptor material 12 of the active layer 5 may be labeled χ _D and χ _A , respectively. The ionization energy of the active layer 5 is defined by the energy difference between the highest occupied molecular orbital (called HO or HOMO) of the active layer ₅ and the vacuum energy level E0, and for the donor material 11 of the active layer 5 and the The acceptor material 12 of the source layer 5 may be labeled _EID and _EIA , respectively. The HO of the donor 11 of the active layer 5 is labeled HO1.

Figure 5 shows a band diagram of a structure corresponding to one embodiment of the present invention. Cathode 3 is characterized by a work function denoted _ΦC . If the cathode 3 is made of ITO, Φ _C =4.7 eV. The characteristics of the electron collection layer 4 are the electron affinity χ ₄ and the ionization energy EI ₄ . If the electron collecting layer 4 is made of ZnO, χ ₄ =4.2 eV, Φ ₁ =4.2 eV and EI ₄ =7.5 eV. The active layer 5 is characterized by the electron affinity χ _D of the donor 11 , the ionization energy EI _D of the donor 11 , the electron affinity χ _A of the acceptor 12 , and the ionization energy EI _A of the acceptor. For the embodiment shown in Figure 3, these energy levels may correspond to χ _D = 3.7 eV, EI _D = 5.15 eV, χ _A = 3.9 eV, and EI _A = 6.0 eV. The hole collecting layer ₆ is characterized by a work function Φ ₆ which may be between 4.9 eV and 5.5 eV if the layer is made of PEDOT:PSS.

The work function of the contacts of the optoelectronic device 1 must be suitable for optimizing the injection and, in particular, in the context of the described application, for the collection of photogenerated charges. Ideally, the work function of the anode 7 is aligned with the HO HO1 of the donor 11 of the active layer 5 and the work function of the cathode 3 is aligned with the LUMO of the acceptor 12 of the active layer 5 .

In an embodiment of the invention, the cathode 3 made of ITO has a work function in the range extending from 4.6 eV to 5 eV (measured for example by a Kelvin probe). Furthermore, most prior art donor materials 11 have ionization potentials in the range extending from 4.6 eV to 5.4 eV. In order to prevent the parasitic injection of holes from the cathode 3 made of ITO into the donor material 11 of the active layer 5, one solution is (for example by depositing a layer between the cathode 3 and the active layer 5, corresponding to the electrons The collection layer 4) reduces the work function of the material in contact with the active layer 5.

In this embodiment of the photovoltaic device 1, the injection of parasitic holes from the cathode 3 into the active layer 5 is prevented, and therefore, the dark current of the photovoltaic device 1 can be minimized or suppressed. Thus, in an embodiment of the present invention, the work function Φ ₁ of the electron collection layer 4 is strictly smaller than the work function Φ _C of the cathode 3 : thus, the injection of parasitic holes can be minimized. Generally speaking, in one embodiment of the invention, in a flip-chip photodiode structure, the electron collection layer 4 enables the formation of one or more potential barriers that prevent the injection of holes from the cathode 3 the active layer 5 . This potential barrier may be at the interface between the active layer 5 and the electron collection layer 4 , and/or at the interface between the electron collection layer 4 and the cathode 3 .

Ethoxylated polyethyleneimine (PEIE) can also be used to make the electron collection layer 4 . In an embodiment of the invention, a layer of evaporated silver may be used as anode 7 and may be _fabricated using a material selected from _PEDOT : _PSS and metal oxides such as _NixOy , _CuxOy or _MoxOy Hole collection layer 6 .

Figure 6 schematically shows a matrix photovoltaic device 8 according to an embodiment of the invention. The matrix optoelectronic device 8 according to the invention comprises a plurality of optoelectronic devices 1 . For example, four optoelectronic devices 1 are shown in FIG. 6 . A matrix photovoltaic device 8 according to an embodiment of the invention includes an electron collection layer 4 that is common to at least a portion of the photovoltaic device 1 and is substantially continuous between each of the photovoltaic devices 1 of the portion. In an embodiment of the invention, in said material of said common electron collecting layer 4, the common electron collecting layer 4 has strictly greater than 10 ⁸ Ω, preferably strictly greater than 10 ¹⁰ Ω and preferably strictly greater than 10 ¹¹ A sheet resistance of Ω and is able to block the current of carriers between the part or parts of the optoelectronic device 1 . In this way, leakage currents between the individual optoelectronic devices 1 of a given matrix can be prevented while depositing a common electron collecting layer 4 without additional photolithographic steps.

In a preferred embodiment of the present invention, the common electron collecting layer 4 is made of ZnO. The thickness of the common electron collecting layer 4 may be greater than 1 nm, preferably between 5 and 500 nm, and preferably between 10 and 40 nm. The common electron collecting layer 4 is deposited, for example, by cathode sputtering.

Figure 7 schematically shows a top view of a matrix photovoltaic device 8 according to an embodiment of the invention. Rows 13 and columns 14 made of conductive material are connected to the TFT matrix 20 enabling multiplexing of the electrical connections between each of the optoelectronic devices 1 and the outside of the matrix optoelectronic devices 8 for biasing and/or collection Electric charge generated by irradiation.

The square grey area shown in FIG. 7 corresponds to the limits of the photovoltaic devices 1 arranged in the grey part. Each TFT 20 is electrically connected to the lower electrode of the matrix photovoltaic device 8, eg the cathode 3, the geometry of which is also defined by the grey squares. The black dashed squares correspond to example deposition areas of the shared electron collecting layer 4 . The illustration is schematic and is intended to enable understanding of the system: millions of cathodes 3 can be covered by a common electron collecting layer 4 .

FIG. 8 schematically shows a cross-sectional view in the thickness direction of the layers of a part of an optoelectronic device 1 comprising an electron collection layer 4 comprising crystallites 16 . The crystallites 16 are arranged in columns in the thickness direction of the electron collection layer 4 . In one embodiment of the invention, the common electron collection layer 4 includes a plurality of crystallites 16 . Advantageously, the material of the electron collecting layer 4 is deposited so as to grow in-line from the cathode 3 . In this way, the lateral conductivity of the electron collection layer 4 (ie in the direction of the principal plane of the electron collection layer 4 ) is limited by the presence of the grain boundaries 17 . In the embodiment shown in FIG. 8 , with respect to the isotropic organization of the material of the electron collecting layer 4 , the electrical conductivity of the electron collecting layer 4 is substantially constant in the thickness direction of the layer. Instead, the resistance in the direction of the main plane of the layer depends on the density of grain boundaries 17 and/or crystallites 16 . The deposition temperature of the material of the electron collecting layer 4 is also a variable on which this lateral resistance depends. The deposition temperature affects the size of the crystallites of the electron collecting layer 4 . In particular, as the size of crystallites 16 increases (eg, as the deposition temperature increases), the density of grain boundaries 17 between crystallites 16 decreases and the lateral resistance decreases. Conversely, if the size of the crystallites 16 is reduced, scattering from the grain boundaries 17 of the crystallites 16 becomes prominent, and the lateral resistance increases. More generally, in embodiments of the present invention, the resistance of the material of the common electron collecting layer 4 in the thickness direction of the electron collecting layer 4 compared to the direction of the principal plane of the electron collecting layer 4 lower rate. More generally, the resistivity of the material of the electron collecting layer 4 is anisotropic in embodiments of the present invention.

In an embodiment of the invention, the work function of the material of the electron collecting layer 4 (eg that of ZnO) is preferably at 4 eV and 4.7 eV for Φ _C = 4.7 eV, χ _D = 3.7 eV, EI _D = 5.15 eV between. The work function of the material below 4.7 eV can ensure the operation of the photovoltaic device 1 or the matrix photovoltaic device 8, and the work function above 4 eV can minimize the injection of parasitic carriers in the photovoltaic device or the matrix photovoltaic device 8 or inhibit.

In general, undoped zinc oxide is considered an n-type semiconductor. The process of deposition of the electron collection layer 4, especially when the material is ZnO, enables the conductive properties of the electron collection layer 4 to be changed. The resistance of the electron collecting layer 4 made of ZnO is between 10 ⁹ and 10 ¹² Ω/□ for deposition at room temperature, and for atmospheres containing more than 1 mass % molecular oxygen, and preferably more than 2 mass % molecular oxygen . For deposition temperatures between 100°C and 400°C, and in the presence of molecular oxygen, the sheet resistance is substantially constant and equal to 1 Ω/□.

More generally, one embodiment of the present invention is a process for fabricating photovoltaic devices 1 and/or matrix photovoltaic devices 8, the process comprising at least one of the following steps: using physical thin film deposition methods such as cathode sputtering at 0°C and The material of the electron collecting layer 4 is deposited at a temperature between 100°C (including 0°C and 100°C) in an atmosphere comprising at least 1% by mass of molecular oxygen and preferably 2% by mass of molecular oxygen.

The resistance of the deposited layer is reduced by annealing (heat treatment) after deposition at a temperature between 0°C and 100°C. For example, for electron collecting layer 4 made of ZnO, heat treatment at temperatures above 200°C results in sheet resistances between 10 Ω/□ and 10 ⁹ Ω/□. This resistance reduction achieved by performing heat treatment can be attributed to the oxidation of ZnO in the presence of air. The resistance of the electron collecting layer 4 can be adjusted by the deposition and annealing process of said layer.

Figure 9 schematically shows thin layers arranged on a substrate of a matrix photovoltaic device 8 according to an embodiment of the invention. Although in one embodiment of the invention the various layers are in direct contact, the various layers are shown separately to enable the schematic to be understood. Depending on the process parameters used in the fabrication of the matrix photovoltaic device 8, the resistivity of the ZnO of the electron collecting layer 4 may not directly depend on the deposition temperature or the temperature of the post-deposition annealing. The resistivity of the material of the electron collection layer 4 may also depend on its environment. For example, in the presence of oxygen, adsorption and desorption processes occur on the surface of the electron collection layer 4 . Oxidizing molecules in gaseous state, such as molecular oxygen, can be adsorbed on the surface of ZnO and converted into negative ions O ₂ ⁻ . This process creates a region depleted of free carriers and reduces the conductivity of the surface of the electron collection layer 4 according to Equation 1:

O ₂ ^(gas) +e ^- →O ₂ ^{- (adsorption)} (1)

In the presence of irradiation, the photogenerated holes can move towards the surface of the electron collection layer 4 and neutralize the negative oxygen ions. According to Equation 2, this results in an increase in conductivity at the surface of the electron collection layer 4:

O ₂ ^- +h ⁺ →O ₂ ^(gas) (2)

As mentioned above, the resistivity and work function of the material of the electron collecting layer 4 are sensitive to light. In order to stabilize the electron collection layer 4, a stabilization layer 10 can be provided on the electron collection layer 4, which has a high stability to light. This stabilizing layer 10 can be made, for example, of tin oxide (SnO _x ) or palladium oxide (PdO _x ), the resistance of which is relatively high, eg strictly greater than 10 ⁸ Ω/□ and preferably strictly greater than 10 ¹⁰ Ω/□. More generally, the stabilization layer 10 may be made of an opaque oxide type material. The thickness of the stabilization layer 10 is, for example, between 1 and 500 nm, and preferably between 10 and 50 nm. Generally speaking, in one embodiment of the invention, the matrix optoelectronic device 8 includes a stabilizing layer 10 disposed between the common electron collecting layer 4 and the at least one active layer 5, the stabilizing layer 10 being able to degrade the common electron collecting layer 4. The dependence of the resistivity of the material on the brightness. In FIG. 9 , each grey square corresponds to a layer deposited to create the matrix photovoltaic device 8 : a stabilization layer 10 is deposited between the common electron collection layer 4 and one or more active layers 5 . In embodiments of the invention, the electron collection layer 4 , the stabilization layer 10 , the active layer 5 and/or the hole collection layer 6 may be common to a part of the photovoltaic devices 1 of the matrix photovoltaic device 8 or to all the photovoltaic devices 1 .

The electron collection layer 4 may be doped with p-type impurities or elements. These elements are, for example, copper, nickel, cobalt, palladium, molybdenum, manganese and/or iron. The presence of p-type impurities in the electron collection layer 4 (made for example of ZnO) makes it possible to limit the conductivity associated with positive carriers (holes) that block current flow and increase the resistance of the material of the electron collection layer 4 . Typically, the common electron collecting layer 4 may comprise p-type elements, and advantageously palladium, cobalt and/or copper, in order to form a p-type semiconductor or insulating oxide such as PdO, CoO or CuO.

In an embodiment of the present invention, the electron collection layer 4 is fabricated using a sol-gel method. The sol-gel deposition method has the advantage of being simple and inexpensive to implement. The implementation of the sol-gel method is described below. In one embodiment of the invention, the process of fabricating photovoltaic device 1 and/or matrix photovoltaic device 8 comprises at least one step of forming said electron collecting layer 4 using a sol-gel method comprising depositing a The step of the solution of the precursor polymer 15. The precursor polymer 15 can be obtained from metal acetates, metal nitrates and/or metal chlorides.

In contrast to sputtering methods performed in partial vacuum, sol-gel methods do not require specific complex equipment. The method consists in coating a substrate with a spin coater or with a printing device (inkjet printing, screen printing) of a solution comprising a solvent and a polymer 15 which is a precursor of the material of the electron collecting layer 4 (eg ZnO). The solvent is then evaporated, and heat treatment can then crystallize the formed layer. Generally, if the temperature of the post-deposition heat treatment is lower than 400°C, the deposited layer is not very dense and has very high resistance. In the case of ZnO formation, the electron collection layer 4 contains ZnO and organic residues left over from synthesis (eg, precursor polymer 15, additives and/or solvents). These synthetic residues influence the conductivity of the electron collection layer 4 .

Figure 10 shows a graph of the change in the concentration of the normalized sol-gel reacted precursor polymer 15 after the post-deposition heat treatment, obtained by gravimetric analysis. More precisely, the ratios shown correspond to 1-(m _f -m _i )/m _i , where m _f is the final mass of the precursor polymer 15 of the given substance, and _mi is the precursor polymer of the given substance 15 initial mass.

Curve (a) (dashed line) represents the ratio as a function of heat treatment temperature for the use of nitrate-type precursor polymer 15 . Curve (b) (dashed line) represents the ratio as a function of heat treatment temperature for the use of acetate-type precursor polymer 15 . Curve (c) (solid line) represents the ratio as a function of heat treatment temperature for the use of chloride-type precursor polymer 15.

Figure 11 schematically shows the effect of the size of the precursor polymer 15 on the distance between the ZnO particles. The chemical nature of the precursor polymer 15 used is a variable that depends on the distance between the various microparticles or aggregates 18 of ZnO formed during the sol-gel process. In general, the resistance of the electron collecting layer 4 varies proportionally with the distance d between the nearest neighbor aggregates 18 of ZnO. In an embodiment of the present invention, the temperature and distance d of the post-deposition heat treatment can be adjusted so that the minimum sheet resistance of the material of the electron collecting layer 4 is greater than 10 ⁸ Ω/□.

FIG. 12 schematically shows the decrease in electrical conductivity in the presence of organic residues 19 in the electron collecting layer 4 . The dashed lines represent the current lines in the aggregates 18 of ZnO: the residues 19 are concentrated at the boundaries between the aggregates 18 . The constrictions formed between the aggregates 18 and the presence of residues 19 in these constrictions tend to make the material more resistive.

In one embodiment of the present invention, a sol-gel deposition method can be used, which can be used as a "complex polymerization method" process. The process includes the following steps:

- adding metal acetate and/or metal nitrate and/or metal chloride to the solvent of 2-methoxyethanol and stirring at 50°C until it dissolves in the solvent;

- Formation of the metal complex by adding ethanolamine acetic acid to the solvent at 70°C. The ions formed are metal and acetate ions;

- waiting during the polymerization reaction, while stirring the solvent at 70°C, until the precursor polymer 15 is obtained;

- Deposition of a solution of precursor polymer 15 on cathode 3 .

The advantage of this process is that it is suitable for the synthesis of complex or mixed oxides from common metal salts such as chlorides, acetates and/or nitrates. Advantageously, the acetate salts described in the preceding paragraphs are chosen to be used in the implementation of the process: they are less sensitive to the presence of water in solution and are therefore more stable. If acetate is used, it is thus not necessary to carry out the process in an inert gas. Advantageously, the acetate salt is formed after partial decomposition of the electrically stable oxide. The use of acetate enables the reproducible manufacture of the electron collection layer 4 . The use of acetic acid makes it possible to avoid the precipitation of metal ions in the second step of the sol-gel method described above, and to increase the service life of the solution to be used for carrying out the sol-gel method. Ethanolamine is a complexing agent and stabilizes and facilitates the polymerization step of the process.

In one embodiment, p-type dopants (Pd, Cu, Ni, Co) may be added during the sol-gel process to reduce the conductivity of the electron collection layer 4 after thermal treatment.

In one embodiment of the invention, the electron collecting layer 4 is formed by depositing ZnO nanoparticles greffées by ethoxylated polyethyleneimine (PEIE). Nanoparticles means particles with a characteristic size (eg diameter of a sphere) between 0.1 nm and 100 nm. Since PEIE is an insulating polymer, the electron collecting layer 4 made with ZnO nanoparticles connected by PEIE has a very high sheet resistance, eg higher than 10 ¹⁰ Ω/□. PEIE can be attached to ZnO microparticles through hydroxyl or amine groups. More generally, optoelectronic device 1 and/or matrix optoelectronic device 8 may comprise metal oxide nanoparticles and polar polymers attached to the metal oxide nanoparticles.

Figure 13 schematically shows a matrix optoelectronic device 8 in which the resistance of the electron collecting layer 4 is increased by producing the layer (forming two types of sublayers) in two deposition steps. The two sublayers are separated by a dashed line in FIG. 13 . A first deposition may be carried out, forming a first sublayer 21 with a thickness of, for example, between 10 nm and 15 nm. This first sublayer 21 is common and is deposited between optoelectronic devices 1 (ie between different pixels). A second deposition may be performed to form a plurality of thicker second sublayers 22 . The deposition of the sublayers 22 takes place in a pattern corresponding to the pattern of the arrangement of the optoelectronic devices 1 . The deposition of the second sublayer 22 can be performed by means of a metal mask etched at the positions corresponding to the optoelectronic device 1 .

In one process of fabricating the matrix photovoltaic devices 8, the thickness of the electron collecting layers 4 between the photovoltaic devices 1 can be reduced, thereby locally increasing the sheet resistance of the electron collecting layers 4.

In one embodiment of the present invention, at least one element selected from the group consisting of substrate 2, cathode 3, electron collecting layer 4, active layer 5, hole collecting layer 6 and anode 7 is transparent.

FIG. 14 shows an embodiment of the present invention in which the matrix optoelectronic device 8 includes a layer 23 of scintillator material. In embodiments of the present invention, a layer 23 of scintillator material may be arranged on each of the anodes 7 of the matrix photovoltaic device 8 . A scintillator material means a material capable of emitting light (eg, in the visible spectrum) after absorbing ionizing radiation (eg, after absorbing x-rays). Advantageously, both the hole collecting layer 6 and the anode 7 are transparent in this embodiment. Thus, the device 8 is capable of imaging x-rays.

In embodiments of the present invention, the detection of x-rays can be performed directly in the active layer. In this case, the substrate 2, cathode 3, electron collection layer 4, hole collection layer 6 and/or anode 7 need not be transparent.

Claims (17)

Claims 1. An optoelectronic device (1) comprising a stack of planar thin layers arranged on an electrically insulating substrate (2), said stack comprising at least: - a cathode (3) made of a material with work function _ΦC ; - an electron collecting layer (4) arranged above said cathode (3) and made of a material with work function Φ ₁ and sheet resistance R; - an active layer (5) comprising at least one p-type organic semiconductor, and an n-type semiconductor, said active layer being suitable for emitting or detecting light and being arranged over said electron collecting layer (4), so The energy level of the highest occupied molecular orbital of the p-type organic semiconductor is HO1; - a hole collecting layer (6) arranged on top of said active layer (5); and - an anode (7) arranged above said hole collecting layer (6); It is characterized by: - the work function Φ1 of the electron collecting layer (4) and the energy level HO1 of the active layer (5) form a capability to prevent the injection of holes from the cathode (3) into the active layer (5) ); and - the sheet resistance R of the electron collecting layer (4) is greater than or equal to 10 ⁸ Ω, - the electron collecting layer (4) is continuous and comprises crystallites (16) arranged in columns in the thickness direction of the electron collecting layer (4), the electron collecting layer (4) The resistivity of the material is lower in the thickness direction of the electron collection layer (4) than in the principal plane direction of the electron collection layer (4). 2. The optoelectronic device (1) according to claim ₁ , wherein the work function Φ1 of the electron collecting layer (4) is strictly smaller than the work function ΦC of the cathode (3 ₎ . 3. The optoelectronic device (1) according to any one of claims 1 or 2, wherein the material of the electron collection layer (4) is selected from zinc oxide and titanium oxide. 4. A matrix optoelectronic device (8) comprising a plurality of optoelectronic devices (1) according to any one of claims 1 to 3 and an electron collection layer (4), the electron collection layer (4) for At least a part of the optoelectronic devices (1) is common and substantially continuous between each of the optoelectronic devices (1). 5. The matrix optoelectronic device (8) according to claim 4, wherein, in the material of the common electron collecting layer (4), the thin layer of the common electron collecting layer (4) The resistance R is able to block the current flow of charge carriers between the part or parts of the optoelectronic device ( 1 ). 6. A matrix optoelectronic device (8) according to claim 4, comprising at least one stabilization layer (10) arranged between the common electron collection layer (4) and at least one active layer (5), Wherein, the stabilization layer (10) can reduce the dependence of the resistivity of the material of the common electron collection layer (4) on the brightness. 7. The matrix photovoltaic device (8) according to claim 6, wherein the material of the stabilization layer (10) is an opaque oxide. 8. The matrix photovoltaic device (8) according to claim 7, wherein the opaque oxide is selected from tin oxide and palladium oxide. 9. The matrix photovoltaic device (8) according to claim 4, wherein the material of the common electron collection layer (4) comprises a p-type dopant. 10. The matrix photovoltaic device (8) according to claim 9, wherein the p-type dopant is selected from the group consisting of palladium, cobalt, copper and molybdenum. 11. The matrix optoelectronic device (8) of claim 4, wherein at least one of the electron collecting layers comprises metal oxide nanoparticles and a polar polymer, the polar polymer being attached to the metal oxide on nanoparticles. 12. The matrix optoelectronic device (8) according to claim 4, wherein a substrate (2), a cathode (3), an electron collection layer (4), an active layer (5), a hole collection layer (6) are selected from the group consisting of ) and at least one element of the anode (7) is transparent. 13. A matrix optoelectronic device (8) according to claim 12, comprising a layer of scintillator material (23) arranged over each of said anodes (7). 14. A process for manufacturing an optoelectronic device (1) according to any one of claims 1 to 3 or a matrix optoelectronic device (8) according to any one of claims 4 to 13, said optoelectronic device The device comprises a stack of planar thin layers arranged on an electrically insulating substrate (2), the stack comprising at least: - a cathode (3) made of a material with work function _ΦC ; - an electron collecting layer (4) arranged above said cathode (3) and made of a material with work function Φ ₁ and sheet resistance R; - an active layer (5) comprising at least one p-type organic semiconductor, and an n-type semiconductor, said active layer being suitable for emitting or detecting light and arranged on top of said electron collecting layer (4), so that The energy level of the highest occupied molecular orbital of the p-type organic semiconductor is HO1; - a hole collecting layer (6) arranged on top of said active layer (5); and - an anode (7) arranged above said hole collecting layer (6), - the electron collecting layer (4) is continuous and comprises crystallites (16) arranged in columns in the thickness direction of the electron collecting layer (4), the electron collecting layer (4) The resistivity of the material is lower in the thickness direction of the electron collection layer (4) than in the principal plane direction of the electron collection layer (4); The process comprises at least one step of depositing the electron collecting layer (4) by cathode sputtering at a temperature between 0°C and 100°C in an atmosphere containing at least 1% by mass molecular oxygen. )s material. 15. A process for manufacturing an optoelectronic device (1) according to any one of claims 1 to 3 or a matrix optoelectronic device (8) according to any one of claims 4 to 13, the optoelectronic device A stack comprising planar thin layers arranged on an electrically insulating substrate (2), the stack comprising at least: - a cathode (3) made of a material with work function _ΦC ; - an electron collecting layer (4) arranged above said cathode (3) and made of a material with work function Φ ₁ and sheet resistance R; - an active layer (5) comprising at least one p-type organic semiconductor, and an n-type semiconductor, said active layer being suitable for emitting or detecting light and arranged on top of said electron collecting layer (4), so that The energy level of the highest occupied molecular orbital of the p-type organic semiconductor is HO1; - a hole collecting layer (6) arranged on top of said active layer (5); and - an anode (7) arranged above said hole collecting layer (6), - the electron collecting layer (4) is continuous and comprises crystallites (16) arranged in columns in the thickness direction of the electron collecting layer (4), the electron collecting layer (4) The resistivity of the material is lower in the thickness direction of the electron collection layer (4) than in the principal plane direction of the electron collection layer (4); The process includes at least one step of forming the electron collecting layer (4) using a sol-gel method, the sol-gel method including the step of depositing a solution comprising a precursor polymer (15), the precursor polymer (15). The bulk polymer (15) is selected from metal acetates, metal nitrates and metal chlorides. 16. The process of claim 15, wherein the solution includes a p-type dopant. 17. A process for manufacturing a matrix optoelectronic device (8) according to any one of claims 4 to 13, said matrix optoelectronic device (8) comprising a plurality of according to claims 1 to 3 arranged in a pattern An optoelectronic device (1) according to any one of the above, comprising a stack of planar thin layers arranged on an electrically insulating substrate (2), the stack comprising at least: - a cathode (3) made of a material with work function _ΦC ; - a common electron collecting layer (4) comprising a first common electron collecting sublayer (21) and a plurality of second sublayers (22), said common electron collecting layer being arranged at said cathode (3) above, and made of a material with a work function of Φ ₁ and a sheet resistance of R; - an active layer (5) comprising at least one p-type organic semiconductor, and an n-type semiconductor, said active layer being suitable for emitting or detecting light and arranged on top of said electron collecting layer (4), so that The energy level of the highest occupied molecular orbital of the p-type organic semiconductor is HO1; - a hole collecting layer (6) arranged on top of said active layer (5); and - an anode (7) arranged above said hole collecting layer (6), - the electron collecting layer (4) is continuous and comprises crystallites (16) arranged in columns in the thickness direction of the electron collecting layer (4), the common electron collecting layer ( 4) the resistivity of the material is lower in the thickness direction of the electron collection layer (4) than in the principal plane direction of the electron collection layer (4); The process comprises at least two sub-steps of depositing the electron collecting layer (4), the at least two sub-steps comprising: - depositing a first common electron collecting sublayer (21); and - depositing a plurality of second sublayers (22) in a pattern corresponding to said pattern of said optoelectronic device (1).

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